basics of in-vehicle networking (ivn) on semiconductor
TRANSCRIPT
Basics of In-Vehicle Networking (IVN)
ON Semiconductor products
Major IVN technologies overview
This presentation deals with basics of LIN, CAN (FD), FlexRay
and automotive Ethernet technologies.
LIN Overview
• LIN = 12 V, single-wire serial communications protocol based
on the common SCI (UART) byte-word interface
• Maximum speed = 20 kb/s (EMC/clock synchronisation)
• Master controls the medium access: no arbitration or collision
management, guaranteed latency times
• Clock synchronization mechanism by slave nodes (no need for quartz or
ceramics resonator)
• Nodes added without HW/SW changes in other slave nodes
• Typically < 12 nodes, (64 identifiers & relatively low transmission speed)
Like in a classroom situation, the
LIN ‘master’ initiates the response
of the other participants
LIN detailsPhysical Layer
• Vsup between 7 V and 18 V
• Strict requirements for slope and symmetry
• Duty-cycle: Min = 39.6%, Max = 58.1% (Bus-load: time-constant between 1 µs and 5
µs: 1k/1 nF 660/6.8 nF 500/10 nF) (not-synchronized oscillator <14% tolerance)
• Communication initiated by the master task (message header)
• Slave task activated upon recognition of identifier - starts the message response (1-8 data bytes + 1
checksum byte)
• Data correctness: parity, checksum
• Identifier = content, not the destination!
• Exchange of data in various ways:
• M → S(s)
• S → M
• S → S(s)
• .message frame
LIN detailsCommunication concept
0 = “dominant” state
1 = “recessive” state
Not used = recessive
LIN Applications
Mirrors, window lift, doors switches, door lock, HVAC motors, control panel, enginesensors, engine cooling fan, seat positioning motors, seat switches, wiper control, lightswitches, interface switches to radio/navigation/phone, rain sensor, light control, sunroof, RF receivers, body computer/smart junction box, interior lighting and more.
Steering Wheel: cruise control,
wiper, turning light, climate
control, radio, telephone
Roof: rain sensor, light sensor,
light control, sun roof
Climate: small motors,
control panel
Engine: sensors,
small motors
Seat: seat position
motors, occupancy
sensor, control panel
Door: mirror, central ECU,
mirror switch, window lift, seat
control switch, door lock
CAN Overview
• Controller Area Network is a fast serial bus designed to
provide an efficient, reliable and very economical link
between sensors and actuators.
• CAN connects the vehicle's electronic equipment
• These connections facilitate the sharing of information and
resources among the distributed applications.
• All nodes can send a message at any time, when two nodes are
accessing the bus together, arbitration decides who will continue.
In CAN communication, all partners are
equal and are able to communicate at
any time. In case of conflicts (two
speaking at the same time), arbitration is
used to ensure messages are
understood.
CAN Applications
• CAN was developed in early 1980’s for automotive and is widely used in all
car parts (Powertrain, Chassis, Body). Every car developed in Europe, USA and
Japan has at least a few CAN nodes; CAN is being adopted in Asia as well.
• An increasing number of products have a CAN transceiver implemented
together with other functionality (e.g. in system basis chips, stepper motors,
park assist,…).
• CAN also found its way into Industrial Applications.
See http://www.can-cia.de/
CAN – detailsCharacteristics
Extended CAN frame (ISO 11898)
• Asynchronous communication (Event Triggered).
• Any node can access the bus when the bus is quiet.
• Non-destructive arbitration, 100% use of the bandwidth
without loss of data, large latency for low priority
messages, low latency for high priority messages.
• Variable message priority based on 11-bit (or extended
29 bit) packet identifier.
• Automatic error detection, signaling and retries.
• CAN uses a twisted pair cable to communicate at
speeds up to 1 Mb/s with up to 40 devices.
CAN – detailsPhysical Layer (*)
• CAN bus requires line termination.
• ISO 11898 standard define the impedance of the cable as 120 ± 12 Ω.
Twisted pair, shielded or unshielded is requested.
(*) Single wire CAN (SEA2411, 33,3 kbit/s) and low speed CAN (ISO11898-3, 125Kbit/s) are not covered by above description
CAN – detailsBus arbitration in more details
• If two messages are simultaneously sent over the CAN bus, the bus takes the “logical AND” of the signal.
• Hence, the messages identifiers with the lowest binary number gets the highest priority.
• Every device listens on the channel and backs off as and when it notices a mismatch between the bus’s bit and its identifier’s bit.
CAN Flexible Data-rate
For increased bandwidth, CAN Flexible Data-rate has been introduced as an extension to CAN
Two techniques are used:1. Increase of the bit rate of the payload2. Increase of the number of bytes in the payload
Flexray Overview
• High data rates (up to 10 Mb/s)
• Time- and event-triggered behavior
• Redundancy
• Fault-tolerance
• Deterministic (use of “time-slots”)As in a train-schedule, all FlexRay traffic on
the bus is nicely scheduled using timeslots.
FlexRay delivers the error tolerance, speed and time-determinism
performance requirements for x-by-wire applications (i.e. drive-by-wire,
steer-by-wire, brake-by-wire, etc.).
Communication cycle
Static Segment: Reserved slots for deterministic data that arrives at a fixed period.
Dynamic Segment: Is used for a wider variety of event-based data that does not require determinism (cfr. CAN).
Symbol Window: Typically used for network maintenance and signaling for starting the network.
Network Idle Time: A known "quiet" time used to maintain synchronization between node clocks.
FlexRay – detailsPhysical Layer
FlexRay – detailsFrame Format
Clock Synchronization
See chapter 8 of FlexRay Protocol Specification
Ethernet Overview: 100Base-T1, 1000Base-T1
• Single twisted pair, full-duplex, 100/1000 Mbps.
• Cable length of up to at least 15 m.
• Differential signal is coupled into a twisted pair via capacitors.
• PHY converts bits to symbols (3 bits -> 2 symbols). Symbol can have value +1, 0
or -1, what corresponds to three different differential voltage levels.
• Peer to peer communication, switches are needed for more complex network.
• To keep synchronization, communication is ongoing even if none of nodes intend
to send data.
Full-duplex channel
Full-duplex channel
Ethernet Overview: 100Base-T1Physical layer details
• One of link partners is Master (initiate training) and the second one is Slave (synchronize its clock with Master’s using clock recovery form data stream).
• As PHY uses PAM3 (3 bits -> 2 symbols) baud rate is 66 MBd/s.
• Both link partners transmits symbols simultaneously, so there might be 5 different differential voltage levels observed.
• Data to be transmitted are combined with side stream scrambler (pseudorandom stream) for better EMC performance (emissions).
Eye diagram of 100Base-T1 link
Ethernet Overview: 10Base-T1S
• 10 Mbps over single twisted pair cable, length of up to at least 15 m.
• Peer to peer half-duplex communication, optionally it can have capability of:
• Full-duplex peer to peer operation
• Half-duplex multidrop (BUS topology like CAN, FlexRay, LIN,…) operation
• Multidrop: One Master, up to at least 8 Slaves. Master initiates communication by
BEACON and then each Slave have an opportunity to send data. This protocol is
called Physical Layer Collision Avoidance (PLCA).